Conventional techniques which may be used to couple light into waveguides include grating coupling and edge coupling.
An example of waveguide coupling, obtained through a grating coupling technology, is disclosed in Chiaretti, C.: “Towards the Industrial Deployment of the Silicon Photonics Technology”, Proc. of the IEEE Bipolar/BiCMOS Circuits and Technology Meeting, 2013.
An example of light coupling into multiple fibers, wherein a fiber V block may be attached to a silicon photonics chip, is disclosed in Narasimha et al.: “An Ultra Low Power CMOS Photonics Technology Platform for H/S Optoelectronic Transceivers at less than $1 per Gbps”, OFC, 2010.
An advantage of grating couplers may lie in that light may exit from a wafer surface, and not from an edge, which facilitates wafer level testing. Grating couplers may also exhibit an advantage in being able to couple to a top surface.
Grating couplers may have one or more disadvantages. For instance, loss over a large wavelength range may be higher away from a center design wavelength, see e.g. Wesley D. Sacher et al.,: “Wide bandwidth and high coupling efficiency Si3N4-on-SOI dual-level grating coupler”, Optical Society of America, 2014.
For instance, a 4-lane Coarse Wavelength Division Multiplexing (CWDM4) may be derived from a PSM4 (Parallel Single Mode 4 lane) specification using e.g. CWDM4 wavelengths: 1271 nm, 1291 nm, 1311 nm, 1331 nm. This type of module may use a single fiber input for transmission (Tx) and a single fiber for reception (Rx), both with e.g. the 4 different “colors” (that is wavelengths) of light. Such an arrangement may provide an advantage for a customer insofar as, instead of, for instance, 4 Tx fibers and 4 Rx fibers (8 in total), the customer may only need to cable two fibers maintaining the quantity, e.g. Gbits, of information transmitted.
However, due to loss in the gratings, which also may be exposed to e.g. process variation and temperature, such an arrangement may not be suitable for broadband CWDM4 applications.
As already discussed previously, another conventional solution is provided by edge coupling. Edge coupling may have a disadvantage in lacking wafer level testing and in optical quality edge finish being possibly required.